Fingerprint sensor and display device including the same

ABSTRACT

A fingerprint sensor includes four transistors and a photodetector. The first transistor connects a second node with a third node based on a voltage of a first node, where the first node corresponding to a first electrode of the photodetector. The second transistor connects the second node with a read-out line based on a scan signal. The third transistor supplies a reset voltage to the first node based on a first reset signal. The fourth transistor connects the first node with the second node based on a second reset signal.

This application claims priority from Korean Patent Application No.10-2020-0104575 filed on Aug. 20, 2020, in the Korean IntellectualProperty Office, the disclosure of which is incorporated by reference inits entirety.

BACKGROUND 1. Field of the Disclosure

One or more embodiments herein relate to a contact sensor for a displaydevice.

2. Description of the Related Art

The demand for display devices continues to increase, especially inelectronic device such as smart phones, digital cameras, laptopcomputers, navigation devices, and smart televisions. These devices mayinclude flat panel displays. Examples include liquid-crystal displays,field emission displays, and organic light-emitting displays. Inaddition to their functionality, display devices may have variousdesigns to meet the requirements of an intended application. Forexample, some display devices may not only include a display panel fordisplaying images, but also an optical sensor for detecting light and afingerprint sensor for detecting a person's fingerprint, as well asother features.

SUMMARY

In accordance with one or more embodiments, a fingerprint sensorachieves improved sensitivity by compensating for threshold voltagecharacteristics of a transistor. Additional embodiments may include adisplay device including such a fingerprint sensor. It should be notedthat objects of the present disclosure are not limited to theabove-mentioned object; and other objects of the present invention willbe apparent to those skilled in the art from the following descriptions.

In accordance with one embodiment, a fingerprint sensor comprising aphotodetector; a first transistor configured to connect a second nodewith a third node based on a voltage of a first node, the first nodecorresponding to a first electrode of the photodetector; a secondtransistor configured to connect the second node with a read-out linebased on a scan signal; a third transistor configured to supply a resetvoltage to the first node based on a first reset signal; and a fourthtransistor configured to connect the first node with the second nodebased on a second reset signal.

In accordance with one embodiment, a display device, comprising adisplay layer configured to emit light to display an image; afingerprint sensor layer on a surface of the display layer, thefingerprint sensor layer comprising a plurality of fingerprint sensors,each of the plurality of fingerprint sensors configured to receivereflected light to generate a sensing signal; and a sensor driverconfigured to receive the sensing signals from the plurality offingerprint sensors through corresponding ones of a plurality ofread-out lines.

Each of the plurality of fingerprint sensors comprises a photodetector;a first transistor configured to connect a second node with a third nodebased on a voltage of a first node that corresponds to a first electrodeof the photodetector; a second transistor configured to connect thesecond node with a corresponding one of the plurality of the read-outlines based on a scan signal; a third transistor configured to supply areset voltage to the first node based on a first reset signal; and afourth transistor configured to connect the first node with the secondnode based on a second reset signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features will become more apparent bydescribing in detail exemplary embodiments thereof with reference to theattached drawings, in which:

FIG. 1 illustrates an embodiment of a display device;

FIG. 2 illustrates an exploded view of the display device;

FIG. 3 illustrates an embodiment of a display panel;

FIG. 4 illustrates a cross-sectional view of a display device accordingto an embodiment;

FIG. 5 illustrates an embodiment of a connection relationship betweenpixels and lines of a display device;

FIG. 6 illustrates an embodiment of a connection relationship betweenfingerprint sensors and lines of a display device;

FIG. 7 illustrates an embodiment of a fingerprint sensor of a displaydevice;

FIG. 8 illustrates an embodiment of signals for the fingerprint sensor;

FIG. 9 illustrates an embodiment of operation of a fingerprint sensorduring a first period;

FIG. 10 illustrates an embodiment of the operation of the fingerprintsensor during a second period;

FIG. 11 illustrates an embodiment of the operation of the fingerprintsensor during a third period;

FIG. 12 illustrates an embodiment of the operation of the fingerprintsensor during a fourth period;

FIG. 13 illustrates an example of a path of reflected light in a displaydevice;

FIG. 14 illustrates an embodiment of a fingerprint pixel and a sensorpixel;

FIG. 15 illustrates an embodiment including an optical layer of adisplay device; and

FIG. 16 illustrates an embodiment of a path of reflected light in adisplay device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, for the purposes of explanation, numerousspecific details are set forth to provide a thorough understanding ofvarious embodiments or implementations of the invention. As used herein“embodiments” and “implementations” are interchangeable words that arenon-limiting examples of devices or methods employing one or more of theinventive concepts disclosed herein. It is apparent, however, thatvarious embodiments may be practiced without these specific details orwith one or more equivalent arrangements. In other instances, well-knownstructures and devices are shown in block diagram form to avoidunnecessarily obscuring various embodiments. Further, variousembodiments may be different, but do not have to be exclusive. Forexample, specific shapes, configurations, and characteristics of anembodiment may be used or implemented in another embodiment withoutdeparting from the inventive concepts.

Unless otherwise specified, the illustrated embodiments are to beunderstood as providing exemplary features of varying detail of someways in which the inventive concepts may be implemented in practice.Therefore, unless otherwise specified, the features, components,modules, layers, films, panels, regions, and/or aspects, etc.(hereinafter individually or collectively referred to as “elements”), ofthe various embodiments may be otherwise combined, separated,interchanged, and/or rearranged without departing from the inventiveconcepts.

The use of cross-hatching and/or shading in the accompanying drawings isgenerally provided to clarify boundaries between adjacent elements. Assuch, neither the presence nor the absence of cross-hatching or shadingconveys or indicates any preference or requirement for particularmaterials, material properties, dimensions, proportions, commonalitiesbetween illustrated elements, and/or any other characteristic,attribute, property, etc., of the elements, unless specified. Further,in the accompanying drawings, the size and relative sizes of elementsmay be exaggerated for clarity and/or descriptive purposes. When anembodiment may be implemented differently, a specific process order maybe performed differently from the described order. For example, twoconsecutively described processes may be performed substantially at thesame time or performed in an order opposite to the described order.Also, like reference numerals denote like elements.

When an element, such as a layer, is referred to as being “on,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, connected to, or coupled to the other element or layer orintervening elements or layers may be present. When, however, an elementor layer is referred to as being “directly on,” “directly connected to,”or “directly coupled to” another element or layer, there are nointervening elements or layers present. To this end, the term“connected” may refer to physical, electrical, and/or fluid connection,with or without intervening elements. Further, the X-axis, the Y-axis,and the Z-axis are not limited to three axes of a rectangular coordinatesystem, such as the x, y, and z axes, and may be interpreted in abroader sense. For example, the X-axis, the Y-axis, and the Z-axis maybe perpendicular to one another, or may represent different directionsthat are not perpendicular to one another. For the purposes of thisdisclosure, “at least one of X, Y, and Z” and “at least one selectedfrom the group consisting of X, Y, and Z” may be construed as X only, Yonly, Z only, or any combination of two or more of X, Y, and Z, such as,for instance, XYZ, XYY, YZ, and ZZ. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

Although the terms “first,” “second,” etc. may be used herein todescribe various types of elements, these elements should not be limitedby these terms. These terms are used to distinguish one element fromanother element. Thus, a first element discussed below could be termed asecond element without departing from the teachings of the disclosure.

Spatially relative terms, such as “beneath,” “below,” “under,” “lower,”“above,” “upper,” “over,” “higher,” “side” (e.g., as in “sidewall”), andthe like, may be used herein for descriptive purposes, and, thereby, todescribe one elements relationship to another element(s) as illustratedin the drawings. Spatially relative terms are intended to encompassdifferent orientations of an apparatus in use, operation, and/ormanufacture in addition to the orientation depicted in the drawings. Forexample, if the apparatus in the drawings is turned over, elementsdescribed as “below” or “beneath” other elements or features would thenbe oriented “above” the other elements or features. Thus, the exemplaryterm “below” can encompass both an orientation of above and below.Furthermore, the apparatus may be otherwise oriented (e.g., rotated 90degrees or at other orientations), and, as such, the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting. As used herein, thesingular forms, “a,” “an,” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. Moreover,the terms “comprises,” “comprising,” “includes,” and/or “including,”when used in this specification, specify the presence of statedfeatures, integers, steps, operations, elements, components, and/orgroups thereof, but do not preclude the presence or addition of one ormore other features, integers, steps, operations, elements, components,and/or groups thereof. It is also noted that, as used herein, the terms“substantially,” “about,” and other similar terms, are used as terms ofapproximation and not as terms of degree, and, as such, are utilized toaccount for inherent deviations in measured, calculated, and/or providedvalues that would be recognized by one of ordinary skill in the art.

Various embodiments are described herein with reference to sectionaland/or exploded illustrations that are schematic illustrations ofidealized embodiments and/or intermediate structures. As such,variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, embodiments disclosed herein should not necessarily beconstrued as limited to the particular illustrated shapes of regions,but are to include deviations in shapes that result from, for instance,manufacturing. In this manner, regions illustrated in the drawings maybe schematic in nature and the shapes of these regions may not reflectactual shapes of regions of a device and, as such, are not necessarilyintended to be limiting.

As customary in the field, some embodiments are described andillustrated in the accompanying drawings in terms of functional blocks,units, and/or modules. Those skilled in the art will appreciate thatthese blocks, units, and/or modules are physically implemented byelectronic (or optical) circuits, such as logic circuits, discretecomponents, microprocessors, hard-wired circuits, memory elements,wiring connections, and the like, which may be formed usingsemiconductor-based fabrication techniques or other manufacturingtechnologies. In the case of the blocks, units, and/or modules beingimplemented by microprocessors or other similar hardware, they may beprogrammed and controlled using software (e.g., microcode) to performvarious functions discussed herein and may optionally be driven byfirmware and/or software. It is also contemplated that each block, unit,and/or module may be implemented by dedicated hardware, or as acombination of dedicated hardware to perform some functions and aprocessor (e.g., one or more programmed microprocessors and associatedcircuitry) to perform other functions. Also, each block, unit, and/ormodule of some embodiments may be physically separated into two or moreinteracting and discrete blocks, units, and/or modules without departingfrom the scope of the inventive concepts. Further, the blocks, units,and/or modules of some embodiments may be physically combined into morecomplex blocks, units, and/or modules without departing from the scopeof the inventive concepts.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure is a part. Terms,such as those defined in commonly used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and should not be interpreted in anidealized or overly formal sense, unless expressly so defined herein.

FIG. 1 is a perspective view of a display device 10 according to anexemplary embodiment, and FIG. 2 is an exploded, perspective view of adisplay device according to an exemplary embodiment.

As used herein, the terms “above,” “top” and “upper surface” refer tothe upper side of the display device 10 (e.g., the side indicated by thearrow in the z-axis direction). The terms “below,” “bottom” and “lowersurface” refer to the lower side of the display device 10 (e.g., theopposite side in the z-axis direction). Also, the terms “left,” “right,”“upper” and “lower” sides indicate relative positions when the displaydevice 10 is viewed from the top. For example, the “left side” refers tothe opposite side of the arrow of the x-axis direction, the “right side”refers to the side indicated by the arrow of the x-axis direction, the“upper side” refers to the side indicated by the arrow of the y-axisdirection, and the “lower side” refers to the opposite side of the arrowof the y-axis direction.

Referring to FIGS. 1 and 2, the display device 10 may include a coverwindow 100, a display panel 300, a bracket 600, a main circuit board700, and a bottom cover 900.

The display device 10 may display video and/or still images. The displaydevice 10 may be used, for example, as the display screen of portableelectronic devices. Examples include mobile phones, smart phones, tabletPCs, smart watches, watch phones, mobile communications terminals,electronic notebooks, electronic books, portable multimedia players(PMPs), navigation devices, and ultra mobile PCs (UMPCs), as well astelevisions, laptop computers, monitors, electronic billboards, and theInternet of Things (IoT) devices, to name a few.

The display device 10 may have a rectangular shape when viewed from thetop. For example, the display device 10 may have a rectangular shapehaving shorter sides in a first direction (x-axis direction) and longersides in a second direction (y-axis direction) when viewed from the top,as shown in FIGS. 1 and 2. Each of the corners where the short side inthe first direction (x-axis direction) meets the longer side in thesecond direction (y-axis direction) may be rounded with a predeterminedcurvature or may be a right angle. The shape of the display device 10(when viewed from the top) is not limited to a rectangular shape, butmay be formed in another shape, e.g., polygonal shape, circular shape,elliptical shape, or another shape.

The cover window 100 may be disposed on the display panel 300 to coverand protect the upper surface of the display panel 300. In oneembodiment, the cover window 100 may include a transmissive area TA,corresponding to a display area DA of the display panel 300, and anon-transmissive area NTA corresponding to a non-display area NDA of thedisplay panel 300. For example, the non-transmissive area NTA may beopaque. In another example, when the non-transmissive area does notdisplay images, it may be formed as a decorative layer having a patternvisible to a user.

The display panel 300 may be disposed under the cover window 100.Accordingly, images displayed by the display panel 300 can be seen fromthe upper surface of the display device 10 through the cover window 100.The display panel 300 may be a light-emitting display panel includinglight-emitting elements. Examples of the display panel 300 include anorganic light-emitting display panel using organic light-emitting diodesincluding organic emissive layer, a micro light-emitting diode displaypanel using micro LEDs, a quantum-dot light-emitting display panel usingquantum-dot light-emitting diodes including an quantum-dot emissivelayer, or an inorganic light-emitting display panel using inorganiclight-emitting elements including an inorganic semiconductor. In thefollowing description, an organic light-emitting display panel isemployed as the display panel 300.

The display panel 300 may include a display area DA and a non-displayarea NDA.

The display area DA may overlaps with the transmissive area TA of thecover window 100 and may include a plurality of pixels for displayingimages. The non-display area NDA may be disposed around the display areaDA and may not display images. For example, the non-display area NDA maysurround the display area DA, but the present disclosure is not limitedthereto. The display area DA may occupy most of the area of the displaypanel 300.

Additionally, the display panel 300 may include a touch electrode layerfor sensing contact from an object, such as a person's finger or astylus pen. In one embodiment, the touch electrode layer may include aplurality of touch electrodes, which may be disposed on a display layeron which a plurality of pixels is disposed.

The display panel 300 may include a display driver 410, a circuit board420, a sensor driver 430, and a touch driver 440. The display driver 410may output signals and voltages for driving the display panel 300. Forexample, the display driver 410 may apply data voltages to data lines,may supply a driving voltage or a supply voltage to a supply voltageline, and may supply a gate control signal to a gate driver.

The circuit board 420 may be attached to pads using an anisotropicconductive film (ACF). Lead lines of the circuit board 420 may beelectrically connected to the pads of the display panel 300. Forexample, the circuit board 420 may be a flexible printed circuit board(FPCB), a printed circuit board (PCB), or a flexible film such as achip-on-film (COF).

The sensor driver 430 may be disposed on the circuit board 420 andelectrically connected to a fingerprint sensor embedded in the displaypanel 300 or a separate fingerprint sensor attached to the display panel300. The sensor driver 430 may convert voltages detected by thelight-receiving elements of the display panel 300 or the photodetectorsattached to the display panel 300 to sensing data (e.g., digital data)and may transmit the sensing data to a main processor 710.

The touch driver 440 may be disposed on the circuit board 420 to measurethe capacitance of the touch electrodes. For example, the touch driver440 may determine whether the existence and position of a user's touchbased on a change in the capacitance of the touch electrodes. Inaccordance with at least one embodiment, a user's touch may refer to thecase where an object (e.g., finger, stylus pen, etc.) contacts a surfaceof the display device 10 disposed on the touch electrode layer. Thetouch driver 440 can determine the position of the user's touch bydistinguishing some touch electrode signals, where the user's touch ismade, from the signals of other touch electrodes where the user's touchis not made.

The bracket 600 may be disposed under the display panel 300 and mayinclude plastic, metal, or a combination thereof. The bracket 600 mayinclude, for example, a first camera hole CMH1 into which a first camerasensor 720 is inserted, a battery hole BH in which a battery isdisposed, and a cable hole CAH through which a cable 415 connected tothe display driver 410 or the circuit board 420 passes.

The main circuit board 700 and the battery 790 may be disposed under thebracket 600 and may be either a printed circuit board (PCB) or aflexible printed circuit board.

The main circuit board 700 may include a main processor 710, a firstcamera sensor 720, and a main connector 730. The first camera sensor 720may be disposed on both the upper and lower surfaces of the main circuitboard 700, the main processor 710 may be disposed on the upper surfaceof the main circuit board 700, and the main connector 730 may bedisposed on the lower surface of the main circuit board 700.

The main processor 710 may control all or a predetermined number of thefunctions of the display device 10. For example, the main processor 710may apply digital video data to the display driver 410 so that thedisplay panel 300 displays images. The main processor 710 may receivesensing data from the sensor driver 430 to generate a fingerprint imageand may recognize the pattern of a user's fingerprint. The mainprocessor 710 may perform authentication according to a user'sfingerprint or run an application. The main processor 710 may receivetouch data from the touch driver 440 to determine coordinates of theuser's touch, and then may run an application indicated by an icondisplayed at the coordinates of the user's touch.

The main processor 710 may convert the first image data input from thefirst camera sensor 720 to digital video data and then output thedigital video data to the display driver 410 through the circuit board420, so that the image captured by the first camera sensor 720 may bedisplayed on the display panel 300.

The first camera sensor 720 may process image frames (e.g., still imageand/or video obtained by an image sensor) and output the processed imageframes to the main processor 710. For example, the first camera sensor720 may be, but is not limited to, a complementary metal oxidesemiconductor (CMOS) image sensor or a charge-coupled device (CCD)sensor. The first camera sensor 720 may be exposed to the lower surfaceof the bottom cover 900 through the second camera hole CMH2 and maycapture an object or a background under the display device 10.

Once having passed through the cable hole CAH of the bracket 600, thecable 415 may be connected to main connector 730. Accordingly, the maincircuit board 700 may be electrically connected to the display driver410 or the circuit board 420.

The battery 790 may be disposed so that it does not overlap the maincircuit board 700 in the third direction (z-axis direction). The battery790 may overlap with the battery hole BH of the bracket 600.

The main circuit board 700 may further include a mobile communicationsmodule to transmit/receive wireless signals to/from at least one of abase station, an external terminal and a server over a mobilecommunications network. The wireless signals may include various typesof data, including but not limited to voice signals, video call signals,and a text/multimedia message transmission/receptions.

The bottom cover 900 may be disposed under the main circuit board 700and the battery 790 and may be fastened and fixed to the bracket 600.The bottom cover 900 may form the exterior of the lower surface of thedisplay device 10 and, for example, may be made of plastic, metal, or acombination thereof.

Additionally, the bottom cover 900 may include a second camera hole CMH2through which the lower surface of the first camera sensor 720 isexposed. The position of the first camera sensor 720 and the positionsof the first and second camera holes CMH1 and CMH2 in line with thefirst camera sensor 720 may different from those shown in FIG. 2.

FIG. 3 is a plan view of a display panel 300 of a display deviceaccording to an exemplary embodiment. Referring to FIG. 3, the displaypanel 300 may include the display area DA and the non-display area NDA.

The display area DA displays images and may include a plurality ofpixels PX. Also, the display area DA may serve as or include a detectorto detect an attribute of an external environment. For example, thedisplay area DA may be a fingerprint recognition area for recognizing auser's fingerprint. The display layer of the display panel 300 mayinclude a plurality of pixels SP. A fingerprint sensor layer of thedisplay panel 300 may include a plurality of fingerprint sensors FPS. Aplurality of pixels SP and a plurality of fingerprint sensors FPS mayoverlap each other in the third direction (z-axis direction) in thedisplay area DA.

Accordingly, the display area DA may be used as an area for recognizinga user's fingerprint, as well as the area for displaying images. Forexample, the display layer of the display panel 300 in which theplurality of pixels SP is arranged and the fingerprint sensor layer ofthe display panel 300 in which the plurality of fingerprint sensors FPSis arranged may overlap each other in the third direction (z-axisdirection).

The non-display area NDA may correspond to all or a portion of theremaining area of the display panel 300, except the display area DA. Thenon-display area NDA may include, for example, a gate driver forapplying gate signals to gate lines, fan-out lines connecting data lineswith the display driver, and pads connected to the circuit board. Forexample, the non-display area NDA may be formed to be opaque and, insome embodiments, may be formed as a decoration layer including apattern visible to a user.

The display panel 300 may further include a sub-area SBA protruding fromone side of the non-display area NDA. The sub-area SBA may protrude fromone side of the non-display area NDA in the opposite direction of thesecond direction (y-axis direction). For example, the length of thesub-area SBA in the first direction (x-axis direction) may be less thanthe length of the display area DA in the first direction (x-axisdirection). The length of the sub-area SBA in the second direction(y-axis direction) may be less than the length of the display area DA inthe second direction (y-axis direction). It is, however, to beunderstood that the present disclosure is not limited thereto. Forexample, the sub-area SBA may be bent and may be disposed under thedisplay panel 300. In such case, the sub-area SBA may overlap thedisplay area DA in the third direction (z-axis direction).

The display driver 410 and the circuit board 420 may be disposed in thesub-area SBA of the display panel 300. The circuit board 420 may beattached on the pads of the sub-area SBA of the display panel 300, forexample, using a low-resistance, high-reliability material (e.g.,anisotropic conductive film (SAP) and self assembly anisotropicconductive paste (SAP)).

FIG. 4 is a cross-sectional view of a display device according to anexemplary embodiment. Referring to FIG. 4, the display panel 300 mayinclude a first substrate SUB1, an optical layer PHL, a display layerDPL, and a fingerprint sensor layer FPSL.

The first substrate SUB1 may be a base substrate or a base member of thedisplay layer DPL and may be made of an insulating material such as apolymer resin. For example, the first substrate SUB1 may be made ofpolyethersulphone (PES), polyacrylate (PAC), polyacrylate (PAR),polyetherimide (PEI), polyethylene naphthalate (PEN), polyethyleneterephthalate (PET), polyphenylene sulfide (PPS), polyallylate (PAR),polyimide (PI), polycarbonate (PC), cellulose triacetate (CTA),cellulose acetate propionate (CAP) or a combination thereof.

In one embodiment, the first substrate SUB1 may be a rigid substrate ora flexible substrate. In this latter case, the first substrate SUB1 maybe bent, folded, or rolled. Also, when the first substrate SUB1 is aflexible substrate, it may be made of polyimide (PI) or another materialthat allows for being, folding, or rolling.

In one embodiment, the first substrate SUB1 may be omitted. In thiscase, the upper surface of the fingerprint sensor layer FPSL may, forexample, be attached directly to the lower surface of the optical layerPHL by an adhesive member OCA. The optical layer PHL may be disposed onthe lower surface of the display layer DPI. In one embodiment, theoptical layer PHL may be disposed between the first substrate SUB1 andthe thin-film transistor layer TFTL to block light incident on thethin-film transistor layer TFTL and an emission material layer EML. Theoptical layer PHL may be made be constructed as a single layer ormultiple layers of one or more of molybdenum (Mo), aluminum (Al),chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd) andcopper (Cu) or an alloy thereof. For another example, the optical layerPHL may be implemented as a black matrix or may be formed of variousmaterials that can block light.

The optical layer PHL may include a plurality of holes H, which mayserve as optical paths through which light travels toward thefingerprint sensor layer FPSL (second light L2), after light emittedfrom the emission material layer EML (first light L1) is reflected bythe user's body. In one embodiment, each of the plurality of holes H maybe a space surrounded by the first substrate SUB1, the inner walls ofthe respective hole H of the optical layer PHL, and the second substrateSUB2. In one embodiment, the plurality of holes H may be filled with thematerial of the second substrate SUB2 during the process of forming thesecond substrate SUB2 on the optical layer PHL. Also, the plurality ofholes H may be optical paths through which the second light L2 travelstoward the fingerprint sensor layer FPSL after the first light Llemitted from the emission material layer EML is reflected by the user'sbody.

The plurality of holes H may not overlap the plurality of thin-filmtransistors of the thin-film transistor layer TFTL, while the opticallayer PHL may overlap the plurality of thin-film transistors of thethin-film transistor layer TFTL. For example, the plurality of holes Hmay be arranged along the first direction (x-axis direction) and thesecond direction (y-axis direction). The size of each of the pluralityof holes H may be determined depending on the path of the second lightL2.

The display layer DPL may include the second substrate SUB2, thethin-film transistor layer TFTL, the emission material layer EML, afirst thin-film encapsulation layer TFEL1, and the touch sensor layerTSL. The second substrate SUB2 may be disposed on the optical layer PHLto support the thin-film transistor layer TFTL. The second substrateSUB2 may be made, for example, of an insulating material such as apolymer resin. Also, the second substrate SUB2 may be a rigid substrateor a flexible substrate that may be bent, folded, or rolled. When thesecond substrate SUB2 is a flexible substrate, it may be made ofpolyimide (PI) or another material that allows for being, folding, orrolling.

For another example, the second substrate SUB2 may be eliminated, andthe thin-film transistor layer TFTL may be disposed directly on theoptical layer PHL.

The thin-film transistor layer TFTL may be disposed above the secondsubstrate SUB2 and may include at least one thin-film transistor fordriving each of the plurality of pixels SP. In one embodiment, the atleast one thin-film transistor of the pixel SP may include asemiconductor layer, a gate electrode, a drain electrode, and a sourceelectrode. For example, the thin-film transistor layer TFTL may furtherinclude gate lines, data lines, power lines, gate control linesconnected to the at least one pixel SPACE, and routing lines connectingpads with data lines.

The emission material layer EML may be disposed on the thin-filmtransistor layer TFTL and may include a light-emitting element connectedto the at least one thin-film transistor of the thin-film transistorlayer TFTL. The light-emitting element may include a first electrode, anemissive layer, and a second electrode. For example, the emissive layermay be, but is not limited to, an organic emissive layer made of anorganic material. When the emissive layer is an organic emissive layer,the thin-film transistor of the thin-film transistor layer TFTL mayapply a predetermined voltage to the first electrode of thelight-emitting element. The second electrode of the light-emittingelement may receive a common voltage or cathode voltage. As a result,holes and electrons may move to the organic emissive layer through ahole transporting layer and a electron transporting layer, respectively,and may then combine in the organic emissive layer to generationemission of light.

The emission material layer EML may include a pixel-defining layerdefining a plurality of pixels SP. The first electrode and the emissivelayer of the light-emitting element may be spaced apart and insulatedfrom each other by the pixel-defining layer.

The first thin-film encapsulation layer TFEL1 may be disposed on theemission material layer EML to cover the thin-film transistor layer TFTLand the emission material layer EML. The first thin-film encapsulationlayer TFEL1 can prevent oxygen or moisture from permeating into theemission material layer EML. For example, the first thin-filmencapsulation layer TFEL1 may include at least one inorganic layer. Thefirst thin film encapsulation layer TFEL1 may include, but is notlimited to, an inorganic film such as a silicon nitride layer, a siliconoxynitride layer, a silicon oxide layer, a titanium oxide layer, or analuminum oxide layer.

The first thin-film encapsulation layer TFEL1 can protect the emissionmaterial layer EML from particles such as dust. The first thin-filmencapsulation layer TFEL1 may include, for example, at least one organicfilm. The first thin-film encapsulation layer TFEL1 may include, but isnot limited to, an organic layer such as an acrylic resin, an epoxyresin, a phenol resin, a polyamide resin or a polyimide resin.

The touch sensor layer TSL may be disposed on the first thin-filmencapsulation layer TFEL1. If the touch sensor layer TSL is disposeddirectly on the first thin-film encapsulation layer TFLE1, the thicknessof the display device 10 can be reduced, compared with a display devicein which a separate touch panel including the touch sensor layer TSL isattached on the first thin-film encapsulation layer TFEL1.

The touch sensor layer TSL may include touch electrodes for sensing auser's touch, and touch electrode lines connected to pads with the touchelectrodes. The touch electrodes of the touch sensor layer TSL may bedisposed in a touch sensing area overlapping the display area DA of thedisplay panel 300.

The cover window 100 may be disposed at the top of the display panel300. In one embodiment, the cover window 100 may be disposed on thetouch sensor layer TSL of the display panel 300. For example, the coverwindow 100 may be attached on the touch sensor layer TSL by an opticallyclear adhesive. The cover window 100 may be in direct contact with auser's finger F or other object.

The fingerprint sensor layer FPSL may be disposed at the bottom of thedisplay panel 300. For example, the fingerprint sensor layer FPSL may beattached under the first substrate SUB1 through an adhesive member(OCA). The adhesive member may be, for example, but is not limited to,an optical clear adhesive (OCA). The upper surface of the firstsubstrate SUB1 may face the display panel 300 or the optical layer PHL,and the lower surface of the first substrate SUB1 may face thefingerprint sensor layer FPSL.

The fingerprint sensor layer FPSL may include a plurality of fingerprintsensors FPS, for example, as shown in FIG. 3. The plurality offingerprint sensors FPS may be connected to the sensor driver 430. Thefingerprint sensors FPS may be optical fingerprint sensors. For example,the fingerprint sensors FPS may be implemented as, but are not limitedto, photo diodes, CMOS image sensors, CCD cameras, photo transistors,etc. The plurality of fingerprint sensors FPS may recognize afingerprint of a finger F by sensing light reflected at the ridges FRand valleys FV between the ridges FR of the finger F.

For example, when the user's finger F is brought into contact with thecover window 100, the first light L1 output from the emission materiallayer EML may be reflected by the ridges FR and/or valleys FV of thefinger F, and the reflected second light L2 may pass through the holes Hof the optical layer PHL to reach the fingerprint sensor layer FPSLdisposed under the first substrate SUB1. The sensor driver 430 candistinguish the second light L2 reflected at the ridges FR of the fingerF from the second light L2 reflected at the valleys FV of the finger Fas received by the fingerprint sensors FPS, to generate sensing data.Then, the sensor driver 430 may transmit the sensing data to the mainprocessor 710, which may generate a fingerprint image based on thesensing data to recognize the pattern of the user's fingerprint.Accordingly, the plurality of holes H of the optical layer PHL may workas paths for the second light L2 reflected by the user's finger F.

By disposing the fingerprint sensor layer FPSL at the bottom of thedisplay panel 300, it is possible to simplify a process of fabricatingthe display device 10, and to prevent a decrease in resolution, becausethe fingerprint sensors FPS are not disposed in the paths through whichthe first light Ll exits, e.g., the upper side of the emission materiallayer EML.

The fingerprint sensor layer FPSL may include a third substrate SUB3, abuffer layer BF, a photodetector layer PDL, and a second thin-filmencapsulation layer TFEL2. The third substrate SUB3 may be a basesubstrate or a base member of the fingerprint sensor layer FPSL and maybe made of an insulating material such as a polymer resin. The thirdsubstrate SUB3 may be a rigid substrate or a flexible substrate that maybe bent, folded, or rolled. When the third substrate SUB3 is a flexiblesubstrate, it may be made of, for example, polyimide (PI) or anothermaterial allowing for bending, folding, or rolling.

The buffer layer BF may be disposed on the third substrate SUB3 and maybe formed of an inorganic film that can prevent or reduce permeation ofair or moisture. For example, the buffer layer BF may include aplurality of inorganic films stacked on one another alternately. Thebuffer layer BF may be made include, but is not limited to, multiplelayers in which one or more inorganic layers (e.g., of a silicon nitridelayer, a silicon oxynitride layer, a silicon oxide layer, a titaniumoxide layer and/or an aluminum oxide layer) are alternately stacked onone another.

The photodetector layer PDL may be disposed on the buffer layer BF andmay include at least one thin-film transistor for driving each of theplurality of fingerprint sensors FPS, and a photodetector connected tothe at least one thin-film transistor. The at least one thin-filmtransistor of the fingerprint sensor FPS may include a semiconductorlayer, a gate electrode, a source electrode, and a drain electrode. Forexample, the photodetector layer PDL may further include scan lines,read-out lines and voltage lines connected to at least one thin-filmtransistor of the fingerprint sensor FPS.

The photodetector may include a first electrode, a photosensitive layer,and a second electrode. The photosensitive layer may include, forexample, but is not limited to, amorphous silicon (a-Si). Thephotosensitive layer may receive the second light L2 and convert theenergy of the second light L2 to an electrical signal (e.g., current orvoltage) generated between the first electrode and the second electrode.

The second thin-film encapsulation layer TFEL2 may be disposed on andcover the upper surface of the photodetector layer PDL and may preventor reduce oxygen or moisture from permeating into the photodetectorlayer PDL. For example, the second thin-film encapsulation layer TFEL2may include at least one inorganic film. The second thin-filmencapsulation layer TFEL2 may include, but is not limited to, aninorganic film such as a silicon nitride layer, a silicon oxynitridelayer, a silicon oxide layer, a titanium oxide layer, or an aluminumoxide layer.

The second thin-film encapsulation layer TFEL2 can protect thephotodetector layer PDL from particles such as dust. For example, thesecond thin-film encapsulation layer TFEL2 may include at least oneorganic film. The second thin-film encapsulation layer TFEL2 mayinclude, but is not limited to, an organic layer such as an acrylicresin, an epoxy resin, a phenol resin, a polyamide resin and a polyimideresin.

In one embodiment, the fingerprint sensor layer FPSL may further includean encapsulation substrate disposed on the second thin-filmencapsulation layer TFEL2. The encapsulation substrate may cover thesecond thin-film encapsulation layer TFEL2 to prevent or reduce air ormoisture from permeating into the fingerprint sensor layer FPSL. Theencapsulation substrate may be, for example, a light-transmittingsubstrate and may be a glass substrate. The encapsulation substrate maybe disposed on the lower surface of the first substrate SUB1 by, but isnot limited to, an adhesive member OCA.

FIG. 5 is a view showing an embodiment of connection relationshipbetween pixels and lines of a display device.

Referring to FIG. 5, a display panel 300 may include a display area DAand a non-display area NDA. The display area DA may include a pluralityof pixels SP, voltage lines VL connected to the pixels SP, gate linesGL, emission lines EL, and data lines DL. Each of the pixels SP may beconnected to at least one gate line GL, at least one data line DL, atleast one emission line EL, and at least one voltage line VL. Forexample, each of the pixels SP may be connected to two gate lines GL,one data line DL, one emission line EL, and one voltage line VL. In oneembodiment, each of the pixels SP may be connected to three or more gatelines GL or a different number of arrangement of the gate lines GL, datalines DL, emission lines EL, and/or voltage lines VL.

In one embodiment, each of the pixels SP may include a drivingtransistor, at least one switching transistor, a light-emitting element,and a capacitor. When a data voltage is applied to the gate electrode,the driving transistor may supply a corresponding driving current to thelight-emitting element so that light is emitted. For example, thedriving transistor and at least one switching transistor may bethin-film transistors. The light-emitting element may emit light havinga certain luminance in proportional to the magnitude of the drivingcurrent of the driving transistor. The light-emitting element may be,for example, an organic light-emitting diode including a firstelectrode, an organic emissive layer, and a second electrode. Thecapacitor can keep the data voltage applied to the gate electrode of thedriving transistor constant.

The pixels SP may receive driving voltage through voltage supply linesVL. The driving voltage may be, for example, a high-level voltage fordriving the light-emitting elements of the pixels SP. The plurality ofvoltage lines VL may be spaced apart from each other in the firstdirection DR1 and may be extended in the second direction DR2. Forexample, the plurality of voltage lines VL may be disposed along columnsof pixels SP disposed in the display area DA, respectively. Each of thevoltage lines VL may be connected to the pixels SP arranged in the samecolumn and may supply driving voltage to the pixels SP.

The gate lines GL and emission lines EL may be extended in the firstdirection (x-axis direction) and may be spaced apart from one another inthe second direction (y-axis direction) intersecting the first direction(x-axis direction). The gate lines GL and the emission lines EL may beformed parallel to each other.

The data lines VL may be spaced apart from each other in the firstdirection DR1 and may be extended in the second direction DR2. The datalines DL may be formed parallel to the voltage lines VL.

The non-display area NDA may correspond to all or a portion of theremaining area of the display panel 300, except the display area DA. Thenon-display area NDA may include a gate driver 450 for applying gatesignals to the gate lines GL, fan-out lines FL connecting the data linesDL with the display driver 410, and pads DP connected to the circuitboard 420. The pads DP may be closer to one edge of the display panel300 than the display driver 410.

The display driver 410 may be connected to the pads DP and may receivedigital video data and timing signals. The display driver 410 mayconvert the digital video data to analog data voltages and may supplythe analog data voltages to the data lines DL through the fan-out linesFOL. For example, the display driver 410 may be implemented as anintegrated circuit (IC) and may be attached on the first substrate SUB1by a chip-on-glass (COG) technique, a chip-on-plastic (COP) technique,or ultrasonic bonding. However, it is to be understood that the presentdisclosure is not limited thereto. The display driver 410 may generate agate control signal and supply the gate control signal to the gatedriver 450 through gate control lines GCL.

The gate driver 450 may be disposed on one side of the non-display areaNDA and may include a plurality of thin-film transistors for generatinggate signals based on the gate control signal. The gate driver 450 maysupply gate signals to the pixels SP through the gate lines GL and mayselect pixels SP to which data voltages are to be applied.

FIG. 6 is a view showing an embodiment of a connection relationshipbetween fingerprint sensors and lines of a display device.

Referring to FIG. 6, the fingerprint sensor layer FPSL may include afingerprint recognition area FPA and a non-fingerprint recognition areaNFPA. The fingerprint recognition area FPA may include a plurality offingerprint sensors FPS, a plurality of scan lines SL connected to thefingerprint sensors FPS, a plurality of read-out lines ROL, and aplurality of supply voltage lines SVL. The plurality of fingerprintsensors FPS may be spaced apart from one another by a distance ranging,for example, from 5 to 50 μm. In one embodiment, each fingerprint pixelon the cover window 100 may include 20 to 30 fingerprint sensors FPS ofthe fingerprint sensor layer FPSL. The number of fingerprint sensors FPSper fingerprint pixel may be different in another embodiment.

The plurality of fingerprint sensors FPS may be connected to the scandriver 460 through the scan lines SL and may receive a scan signal fromthe scan driver 460. The scan lines SL may extend in the first direction(x-axis direction) and may be spaced apart from each other in the seconddirection (y-axis direction). The scan driver 460 may supply a scansignal to each of the plurality of fingerprint sensors FPS to selectfingerprint sensors FPS and to sense a change in the sensing signal.

The fingerprint sensors FPS may be connected to the fingerprint pads FPthrough the read-out lines ROL. The fingerprint pads FP may be connectedto the sensor driver 430. The fingerprint sensors FPS may supply sensingsignals to the sensor driver 430 through the read-out lines ROL. Theread-out lines ROL may be spaced apart from each other in the firstdirection (x-axis direction) and may be extended in the second direction(y-axis direction).

The non-fingerprint recognition area NFPA may be disposed on the outerside of the fingerprint recognition area FPA. The non-fingerprintrecognition area NFPA may be defined as an area of the fingerprintsensor layer FPSL different from the fingerprint recognition area FPA.For example, the scan driver 460 may be disposed on one side of thenon-fingerprint recognition area NFPA and may be connected to the scanlines SL extended to the fingerprint recognition area FPA.

When a user's finger F is brought into contact with the cover window100, the fingerprint sensor FPS that has received the scan signal mayoutput a changed sensing signal. The sensing signal of the fingerprintsensor FPS that has received light reflected by the ridges FR of thefinger F may be different from the sensing signal of the fingerprintsensor FPS that has received the light reflected by valleys FV of thefinger F. The sensor driver 430 may generate sensing data by identifyingor otherwise based on such a difference between the sensing signals. Themain processor 710 may determine whether the ridges FR or valleys FV ofthe finger F are brought into contact with the fingerprint pixel, of thecover window 100 corresponding to the fingerprint sensor FPS, based onthe sensing data. Accordingly, the main processor 710 can recognize thepattern of a user's fingerprint based on the sensing data.

The non-fingerprint recognition area NFPA may further includefingerprint recognition pads FP at one edge of the fingerprint sensorlayer FPSL. The fingerprint recognition pads FP may be connected to thesensor driver 430 to supply a signal applied from an external integratedcircuit to the sensor driver 430. In one embodiment, the display layerDPL and the fingerprint sensor layer FPSL may have the same size whenviewed from the top, but these sizes may be different in anotherembodiment. In one embodiment, the size of the fingerprint sensor layerFPSL may be equal to the size of part of the display layer DPL.

FIG. 7 is a circuit diagram of a fingerprint sensor FPS of a displaydevice according to an exemplary embodiment.

Referring to FIG. 7, the fingerprint sensor FPS may include first tosixth transistors ST1 to ST6, a photodetector PD, and a capacitor Cl.The first transistor ST1 may include a gate electrode connected to afirst node N1, a source electrode connected to a third node N3, and adrain electrode connected to a second node N2. The first transistor ST1may control a source-drain current Isd (hereinafter referred to as asensing current) based on the voltage of the first node N1 that is thefirst electrode of the photodetector PD. The sensing current Isd flowingthrough the channel of the first transistor ST1 may be proportional tothe square of the difference between the threshold voltage Vth and thevoltage Vsg between the source electrode and the gate electrode of thefirst transistor ST1 (Isd=k′×(Vsg−Vth)²), where k′ denotes aproportional coefficient determined by the structure and physicalproperties of the first transistor ST1, Vsg denotes the source-gatevoltage of the first transistor ST1, and Vth denotes the thresholdvoltage of the first transistor ST1.

The second transistor ST2 may be turned on by a scan signal of the scanline SL(n), to connect the second node N2 (corresponding to the drainelectrode of the first transistor ST1) with the read-out line ROL. Thegate electrode of the second transistor ST2 may be connected to the scanline SL(n), the source electrode may be connected to the second node N2,and the drain electrode may be connected to the read-out line ROL. Thesource electrode of the second transistor ST2 may be connected to thedrain electrode of the first transistor ST1 and the source electrode ofthe fourth transistor ST4 through second node N2.

The third transistor ST3 may be turned on by a first reset signal of afirst reset line RSL(n), to supply a reset voltage VR to the first nodeN1. The third transistor ST3 may have a gate electrode connected to thefirst reset line RSL(n), a source electrode connected to a reset voltageline, and a drain electrode connected to the first node N1.Additionally, the drain electrode of the third transistor ST3 may beconnected to the first electrode of the photodetector PD, the gateelectrode of the first transistor ST1, and the drain electrode of thefourth transistor ST4 through the first node N1.

The fourth transistor ST4 may be turned on by a second reset signal of asecond reset line RSL(n+1), to connect the first node N1 with the secondnode N2. The fourth transistor ST4 may have a gate electrode connectedto the second reset line RSL(n+1), a source electrode connected to thesecond node N2, and a drain electrode connected to the first node N1.Additionally, the source electrode of the fourth transistor ST4 may beconnected to the drain electrode of the first transistor ST1 and thesource electrode of the second transistor ST2 through the second nodeN2. Also, the drain electrode of the fourth transistor ST4 may beconnected to the first electrode of the photodetector PD, the gateelectrode of the first transistor ST1, and the drain electrode of thethird transistor ST3 through the first node N1.

The fifth transistor ST5 may be turned on by the scan signal of the scanline SL(n), to apply a common voltage VC to the third node N3 thatcorresponds to the source electrode of the first transistor ST1. Forexample, the common voltage VC may be, for example, a high-levelvoltage. The fifth transistor ST5 may have a gate electrode connected tothe scan line SL(n), a source electrode connected to a common voltageline, and a drain electrode connected to the third node N3.Additionally, the drain electrode of the fifth transistor ST5 may beconnected to the source electrode of the first transistor ST1 and thedrain electrode of the sixth transistor ST6 through the third node N3.

The sixth transistor ST6 may be turned on by the second reset signal ofthe second reset line RSL(n+1), to apply a sampling voltage VS to thethird node N3 that corresponds to the source electrode of the firsttransistor ST1. The sixth transistor ST6 may have a gate electrodeconnected to the second reset line RSL(n+1), a source electrodeconnected to a sampling voltage line, and a drain electrode connected tothe third node N3. Additionally, the drain electrode of the sixthtransistor ST6 may be connected to the source electrode of the firsttransistor ST1 and the drain electrode of the fifth transistor ST5through the third node N3.

The photodetector PD may recognize the pattern of a user's fingerprintbased on the second light L2 reflected by a user's finger F. Thephotodetector PD may have a first electrode connected to the first nodeN1 that corresponds to the gate electrode of the first transistor ST1and the second electrode connected to a bias voltage line. The secondelectrode of the photodetector PD may receive a bias voltage VB from thebias voltage line. The bias voltage VB may be, for example, a low-levelvoltage. The first capacitor C1 may be disposed between the firstelectrode and the second electrode of the photodetector PD, to preventexcessive current from flowing in the photodetector PD.

The photodetector PD may not receive light, for example, if an object(e.g., user's finger) does not physically contact the cover window 100.The fingerprint sensor FPS may apply a reverse bias between the firstelectrode and the second electrode of the photodetector PD. In oneembodiment, reverse bias may refer to the case where the voltage of thefirst node N1 (which corresponds to the first electrode of aphotodetector PD) is greater than the bias voltage VB applied to thesecond electrode of the photodetector PD. If the photodetector PDreceives no light, the photodetector PD may have a voltage in thereverse direction between the first electrode and the second electrode,and the photodetector PD may cut off a current between the first node N1and the bias voltage line.

When a user's finger F is brought into contact with the cover window100, the photodetector PD may receive the second light L2 reflected bythe ridges FR and/or the valleys FV of the finger F. The first light L1output from the emission material layer EML is reflected by the ridgesFR and/or the valleys FV of the finger F, and the reflected second lightL2 may reach the photodetector PD of the fingerprint sensor layer FPSL.The photodetector PD may convert the energy of the second light L2 to anelectrical signal (e.g., current or voltage) formed between the firstelectrode and the second electrode. The converted electrical signal maythen flow from the first node N1 to the bias voltage line.

For example, when a reverse bias is applied between the first electrodeand the second electrode of the photodetector PD, a current in thereverse direction, proportional to the amount of the second light L2,may flow in the photodetector PD. Thus, the voltage of the first node N1may be decreased. Accordingly, when the photodetector PD receives thesecond light L2, the voltage of the first node N1 may be reduced and themagnitude of the sensing current (or the source-drain current) of thefirst transistor ST1 may be reduced. The sensing current of the firsttransistor ST1 may pass through the second transistor ST2 and may beapplied to the sensor driver 430 as a sensing signal.

The sensor driver 430 may generate sensing data based on the sensingsignal received from the fingerprint sensors FPS. The main processor 710may determine whether the sensing data corresponds to the ridges FRand/or the valleys FV of the finger F, thereby recognizing the patternof a user's fingerprint.

The photodetector PD may be implemented as, for example, a phototransistor or a photo diode. The photodetector PD may be an opticalsensor that converts light energy to electrical energy and may utilize aphotovoltaic effect (e.g., a change of current flowing therein)depending on the intensity of light.

FIG. 8 is a waveform diagram of signals that may be supplied to thefingerprint sensor of FIG. 7 in accordance with one embodiment. FIG. 9is a diagram showing an embodiment of an operation of a fingerprintsensor during a first period in a display device according to anexemplary embodiment. FIG. 10 is a diagram showing an embodiment of anoperation of the fingerprint sensor during a second period in thedisplay device according to the exemplary embodiment. FIG. 11 is adiagram showing an embodiment of an operation of the fingerprint sensorduring a third period in the display device according to the exemplaryembodiment. FIG. 12 is a diagram showing an embodiment of an operationof a fingerprint sensor during a fourth period in a display deviceaccording to an exemplary embodiment.

Referring to FIGS. 8 to 12, the fingerprint sensor FPS may be connectedto a first reset line RSL(n), a second reset line RSL(n+1), and a scanline SL(n). When the fingerprint sensors FPS are driven at apredetermined frequency, one frame may include first to fourth periodst1 to t4.

Referring to FIG. 9 in conjunction with FIG. 8, the first reset lineRSL(n) may supply a first reset signal RST(n) at a gate-on level duringthe first period t1. The third transistor ST3 may be turned on duringthe first period t1 based on the first reset signal RST(n), and maysupply the reset voltage VR to the first node N1. Accordingly, the firstnode N1 (which corresponds to the gate electrode of the first transistorST1) may be reset by reset voltage VR.

Referring to FIG. 10 in conjunction with FIG. 8, the second reset lineRSL(n+1) may supply a second reset signal RST(n+1) at the gate-on levelduring a second period t2 after the first period t1. The sixthtransistor ST6 may be turned on during the second period t2 based on thesecond reset signal RST(n+1), and may supply the sampling voltage VS tothe third node N3. Immediately after the sixth transistor ST6 is turnedon, the second node N2 (which corresponds to the source electrode of thefirst transistor ST1) may have the sampling voltage VS, and the firstnode N1 (which corresponds to the gate electrode of the first transistorST1) may have the reset voltage VR.

In one embodiment, the sampling voltage VS may be greater than the resetvoltage VR. In such case, the voltage Vsg between the source electrodeand the gate electrode of the first transistor ST1 (or the differencebetween the voltage of the second node N2 and the voltage of the firstnode N1) may be greater than the threshold voltage Vth of the firsttransistor ST1, to thereby turn on the first transistor ST1. Inaddition, the fourth transistor ST4 may be turned on during the secondperiod t2 based on the second reset signal RST(n+1), and may connect thesecond node N2 to the first node N1. Accordingly, the first transistorST1 may be turned on until the gate electrode of the first transistorST1 reaches the difference voltage VS-Vth between the sampling voltageVS and the threshold voltage Vth. As a result, the first node N1 (thatcorresponds to the gate electrode of the first transistor ST1) may besampled by the sampling voltage VS.

Referring to FIG. 11 in conjunction with FIG. 8, the photodetector PDmay receive light during a third period t3 after the second period t2.For example, the photodetector PD may not receive light if there is nophysical contact of an object on the cover window 100. In this case, thefingerprint sensor FPS may apply a reverse bias between the firstelectrode and the second electrode of the photodetector PD. In oneembodiment, the reverse bias refer to the case where the voltage of thefirst node N1 (which is the first electrode of a photodetector PD) isgreater than the bias voltage VB applied to the second electrode of thephotodetector PD. If the photodetector PD receives no light, thephotodetector PD may have a voltage in the reverse direction between thefirst electrode and the second electrode, and the photodetector PD cancut off current between the first node N1 and the bias voltage line.

When an object (e.g., user's finger F) is brought into contact with thecover window 100, the photodetector PD may receive the second light L2reflected by the ridges FR and/or the valleys FV of the finger F. Thefirst light Ll output from the emission material layer EML is reflectedby the ridges FR and/or the valleys FV of the finger F, and thereflected second light L2 may reach the photodetector PD of thefingerprint sensor layer FPSL. The photodetector PD may convert theenergy of the second light L2 to an electrical signal (e.g., current orvoltage) formed between the first electrode and the second electrode.The converted electrical signal may then flow from the first node N1 tothe bias voltage line.

For example, when a reverse bias is applied between the first electrodeand the second electrode of the photodetector PD, current may flow inthe photodetector PD in the reverse direction in an amount proportionalto the amount of the second light L2. Thus the voltage of the first nodeN1 may be decreased. Accordingly, when the photodetector PD receives thesecond light L2, the voltage of the first node N1 may be reduced and themagnitude of the sensing current (or the source-drain current) of thefirst transistor ST1 that flows during a fourth period t4 may bereduced. The sensing current of the first transistor ST1 may passthrough the second transistor ST2 and may be applied to the sensordriver 430 as a sensing signal during the fourth period t4.

Referring to FIG. 12 in conjunction with FIG. 8, the scan line SL(n) maysupply the scan signal SC(n) at the gate-on level during the fourthperiod t4 after the third period t3. The fifth transistor ST5 may beturned on during the fourth period t4 based on the scan signal SC(n),and may apply the common voltage VC to the third node N3. The firsttransistor STI may output a sensing current (or a source-drain current)based on the voltage of the first node N1.

For example, when the intensity of reflected light incident on thephotodetector PD is relatively small, the magnitude of the sensingcurrent may be relatively large. When the intensity of reflected lightincident on the photodetector PD is relatively large, the magnitude ofthe sensing current may be relatively small. The second transistor ST2may be turned on during the fourth period t4 based on the scan signalSC(n), and may connect the second node N2 with the read-out line ROL.Accordingly, the second transistor ST2 may supply the sensing currentoutput from the first transistor ST1 to the read-out line ROL. Thefingerprint sensor FPS may supply a sensing signal Rx by a sensingcurrent to the sensor driver 430 through the read-out line ROL.

The sensor driver 430 may generate sensing data based on the sensingsignal Rx received from the fingerprint sensors FPS. The main processor710 may determine whether the sensing data corresponds to the ridges FRand/or the valleys FV of the finger F, thereby recognizing the patternof a user's fingerprint.

Using the fingerprint sensors FPS (each of which, may include, in onenon-limiting embodiment, first to sixth transistors ST1 to ST6 and thephotodetector PD), the threshold voltage Vth characteristics of thefirst transistor ST1 of each of the fingerprint sensors FPS can becompensated for. For example, if the magnitude of the current flowinginto the first transistor ST1 during the fourth period t4 is 1 μA orless, the magnitude of the sensing current corresponding to the ridgesFR of the finger F can be clearly distinguished from the magnitude ofthe sensing current corresponding to the valleys of the finger F. Themagnitudes of the current flowing into the first transistor ST1 may bedifferent in another embodiment. Accordingly, the display device maycompensate for dispersion of the first transistors of the plurality offingerprint sensors by maintaining the voltage of the gate electrode ofthe first transistor connected to the photodetector PD. This may resultin a substantial improvement in sensitivity of the fingerprint sensors.

FIG. 13 is a perspective view showing a path of reflected light in adisplay device according to an exemplary embodiment. FIG. 14 is adiagram illustrating a fingerprint pixel and a sensor pixel of a displaydevice according to an exemplary embodiment.

Referring to FIGS. 13 and 14 in view of FIG. 1, the display device 10may include a cover window 100, a display layer DPL, an optical layerPHL, and a fingerprint sensor layer FPSL. The cover window 100 mayinclude a plurality of fingerprint pixels FPP and a plurality ofsampling regions SPR surrounding the fingerprint pixels FPP,respectively. The fingerprint sensor layer FPSL may include a pluralityof fingerprint sensors FPS and a plurality of sensing regions SSR eachincluding a plurality of fingerprint sensors FPS and corresponding toone fingerprint pixel FPP and one hole H.

One fingerprint pixel FPP on the cover window 100 may correspond to atleast one fingerprint sensor FPS of the fingerprint sensor layer FPSL.One fingerprint pixel may correspond to, for example, 20 to 30fingerprint sensors FPS, but may correspond to a different number offingerprint sensors FPS in another embodiment. The sampling region SPRon the cover window 100 may correspond to sensing region SSR of thefingerprint sensor layer FPSL.

Each of the plurality of fingerprint pixels FPP may correspond to arespective one of the holes H of the optical layer PHL. In addition,each of the plurality of sensing regions SSR may correspond to one holeH of the optical layer PHL. For example, when the user's finger F isbrought into contact with the cover window 100, each of the plurality ofsampling regions SPR may reflect the first light L1 output from thedisplay panel 300 and the second light L2 (reflected by each of thesampling regions SPR) may pass through a hole H of the optical layer PHLto reach the sensing region SSR of the fingerprint sensor layer FPSL.The plurality of holes H of the optical layer PHL may therefore serve aspaths for the second light L2 reflected by the user's finger F. As aresult, the plurality of fingerprint sensors FPS may sense the secondlight L2 reflected by the ridges FR and/or the valleys FV between theridges FR of the finger F in contact with the sampling region SPR on thecover window 100.

The plurality of fingerprint sensors FPS may sense the second light L2reflected by the ridges FR and/or the valleys FV of the finger F togenerate a sensing signal. The sensing signal may then be supplied tothe sensor driver 430. The sensor driver 430 may distinguish between asensing signal corresponding to the ridges FR of the finger F and asensing signal corresponding to the valleys FV of the finger F.Accordingly, the sensor driver 430 may merge sensing signals of thefingerprint sensors FPS to recognize a fingerprint pattern of a fingerin contact with the sampling region SPR.

Each of the plurality of sensing regions SSR may include a central areaCA and a surrounding area SA. The central area CA may include at leastone fingerprint sensor FPS disposed in the center of the sensing regionSSR. The second light L2 reflected by the user's finger F may mostlyreach the central area CA. Accordingly, user's fingerprint informationmay be concentrated on at least one fingerprint sensor FPS of thecentral area CA.

The surrounding area SA may surround the central area CA and may includeat least one fingerprint sensor FPS surrounding the central area CA. Forexample, some of the fingerprint sensors FPS in the surrounding area SAmay receive the reflected second light L2, and some others of thefingerprint sensors FPS in the surrounding area SA may not receive thereflected second light L2. In one embodiment, the average intensity ofthe second light L2 reaching the fingerprint sensor FPS of thesurrounding area SA may be less than the average intensity of the secondlight L2 reaching the fingerprint sensor FPS of the central area CA.Accordingly, the reflected second light L2 may reach relatively less thesurrounding area SA. Although the fingerprint sensor FPS in thesurrounding area SA may contain user's fingerprint information, it mayinclude relatively less information than the fingerprint sensor FPS inthe central area CA.

The display device 10 can sense the light reflected by the user's fingerF through the fingerprint sensors FPS by adjusting the ratio between afingerprint distance OD and a sensor distance ID. The fingerprintdistance OD may refer to the distance between the surface of the coverwindow 100 (with which the user's finger F is in contact) and the centerpoint of the hole H of the optical layer PHL. The sensor distance ID mayrefer to the distance between the center point of the hole H of theoptical layer PHL and the fingerprint sensor FPS of the fingerprintsensor layer FPSL.

For example, light reflected from one end of the fingerprint pixel FPPon the cover window 100 may pass through the central point of the hole Hto reach one end of the fingerprint sensor FPS. In addition, lightreflected from the opposite end of the fingerprint pixel FPP on thecover window 100 may pass through the central point of the hole H toreach the other end of the fingerprint sensor FPS. Accordingly, theshape of the fingerprint directly in contact with the fingerprint pixelFPS and the image formed on the fingerprint sensor FPS may differ by 180degrees. The sensor driver 430 may generate a fingerprint image byinverting the image formed on the fingerprint sensor FPS. In accordancewith one embodiment, the display device 10 can improve the sensitivityof the fingerprint sensors FPS by adjusting the ratio between thefingerprint distance OD and the sensor distance ID and adjusting thearrangement and shape of the holes H of the optical layer PHL.

FIG. 15 is a plan view showing a light-blocking layer of a displaydevice according to an exemplary embodiment. Referring to FIG. 15, theoptical layer PHL may include a plurality of holes H having, forexample, a circular shape. The diameter r of each of the holes H mayrange, for example, from 3 to 20 μm, but the diameter may lie in adifferent range in another embodiment.

The plurality of holes H may be arranged in the first direction (x-axisdirection) to have a first pitch P1. The first pitch P1 may be, forexample, 1.3 to 1.5 times the sensor distance ID, and in one case may be1.3 times the sensor distance ID. The first pitch P1 may be different inanother embodiment. The sensor distance ID may refer to the distancebetween the center point of the hole H of the optical layer PHL and thefingerprint sensor FPS of the fingerprint sensor layer FPSL.

The plurality of holes H may be arranged in the second direction (y-axisdirection) to have a second pitch P2. The second pitch P2 may be equalto or different from the first pitch P1. The plurality of holes H may bearranged, for example, in parallel in the first direction (x-axisdirection) and the second direction (y-axis direction). In oneembodiment, the plurality of holes H may be arranged along the firstpitch P1 and the second pitch P2, and may be aligned in directions otherthan the first direction (x-axis direction) and/or the second direction(y-axis direction).

In one embodiment, the first pitch P1 or the second pitch P2 may beproportional to the thickness of the first thin-film encapsulation layerTFEL1. As the thickness of the first thin-film encapsulation layer TFEL1increases, the fingerprint distance OD may increase, and so may theareas of the fingerprint pixel FPP and the sampling area SPR. The firstpitch P1 or the second pitch P2 of the plurality of holes H may beproportional to the thickness of the first thin-film encapsulation layerTFEL1 to adjust the ratio between the fingerprint distance OD and thesensor distance ID.

For example, the first pitch P1 or the second pitch P2 may beproportional to the distance between the light-emitting elements of theemission material layer EML or the distance between the pixels SP. Asthe distance between the light-emitting elements increases, the distancebetween the second lights L2 reflected by the finger F may alsoincrease. Accordingly, the first pitch P1 or the second pitch P2 may beproportional to the distance between light-emitting elements or thedistance between pixels SP so the plurality of holes H work as paths forthe second lights L2.

The optical layer PHL may include first to fourth holes H1, H2, H3 andH4 adjacent to each other. For example, the first to fourth holes H1,H2, H3 and H4 of the optical layer PHL may be close to one another(e.g., less than a predetermined distance), and the sensing regions SSRcorresponding to the first to fourth holes H1, H2, H3 and H4 of theoptical layer PHL, respectively, may also be close to one another (e.g.,less than a predetermined distance). Therefore, the second lights L2reflected by the user's finger F may pass through the first to fourthholes H1, H2, H3 and H4 to mostly reach the sensing regions SSR close toeach other.

The shape of the plurality of holes H is not limited to the circularshape shown in FIG. 15. In another embodiment, the plurality of holes Hmay have an elliptical shape, a polygonal shape or another shape, or acombination of different shapes. For example, in one embodiment, theplurality of holes H may have different shapes in the optical layer PHL.

FIG. 16 is a cross-sectional view showing a path of reflected light in adisplay device according to an exemplary embodiment. Referring to FIG.16, the display device 10 may include a first substrate SUB1, an opticallayer PHL, a second substrate SUB2, a thin-film transistor layer TFTL,an emission material layer EML, and a first thin-film encapsulationlayer TFEL1, a touch sensor layer TSL, a cover window 100, a thirdsubstrate SUB3, a buffer layer BF, a photodetector layer PDL, and asecond thin-film encapsulation layer TFEL2.

The first substrate SUB1 may be a base substrate or a base member of thedisplay layer DPL and may be made of an insulating material such as apolymer resin. The first substrate SUB1 may be a rigid substrate or aflexible substrate that may be bent, folded, or rolled. When the firstsubstrate SUB1 is a flexible substrate, it may be made of polyimide (PI)or another material that allows for bending, folding, or rolling.

The optical layer PHL may cover the lower surface of the thin-filmtransistor layer TFTL and may be disposed between the first substrateSUB1 and the thin-film transistor layer TFTL, to block light incident onthe thin-film transistor layer TFTL and an emission material layer EML.The optical layer PHL may include a plurality of holes H, which mayserve as optical paths through which reflected light travels toward thefingerprint sensor layer FPSL (second light L2). The light L2 may beinitially emitted from the emission material layer EML (first light L1)and then reflected from the object (e.g., finger of the user's body).

The second substrate SUB2 may be disposed on the optical layer PHL tosupport the thin-film transistor layer TFTL. The second substrate SUB2may be made of an insulating material, e.g., a polymer resin.

The thin-film transistor layer TFTL may be disposed above the secondsubstrate SUB2 and may include at least one thin-film transistor 310 fordriving each of the plurality of pixels SP. The thin-film transistorlayer TFTL may further include a gate insulator 321, an interlayerdielectric layer 323, a protective layer 325, and a planarization layer327. At least one thin-film transistor 310 may include a semiconductorlayer 311, a gate electrode 312, a source electrode 313 and a drainelectrode 314.

The semiconductor layer 311 may be disposed on the second substrate SUB2and may be disposed to overlap the gate electrode 312, the sourceelectrode 313, and the drain electrode 314. The semiconductor layer 311may be in direct contact with the source electrode 313 and the drainelectrode 314, and may face the gate electrode 312 with the gateinsulator 321.

The gate electrode 312 may be disposed on the gate insulator 321 and mayoverlap the semiconductor layer 311, with the gate insulator 321interposed therebetween.

The source electrode 313 and the drain electrode 314 are disposed on theinterlayer dielectric layer 323 and spaced apart from each other. Thesource electrode 313 may be in contact with one end of the semiconductorlayer 311 through a contact hole formed in the gate insulator 321 andthe interlayer dielectric layer 323. The source electrode 313 may be incontact with the other end of the semiconductor layer 311 through acontact hole formed in the gate insulator 321 and the interlayerdielectric layer 323. The drain electrode 314 may be in direct contactwith a first electrode 331 of the light-emitting element 330 through acontact hole of the protective layer 325.

The gate insulator 321 may be disposed over the semiconductor layer 311.For example, the gate insulator 321 may be disposed over thesemiconductor layer 311 and on the second substrate SUB2 and mayinsulate the semiconductor layer 311 from the gate electrode 312. Thegate insulator 321 may include a contact hole penetrating through thesource electrode 313 and a contact hole penetrating through the drainelectrode 314.

The interlayer dielectric layer 323 may be disposed on the gateelectrode 312. For example, the interlayer dielectric layer 323 mayinclude the contact hole through which the source electrode 313 passesand the contact hole through which the drain electrode 314 passes. Thecontact holes of the interlayer dielectric layer 323 may be connected tothe contact holes of the gate insulator 321.

The protective layer 325 may be disposed on the thin-film transistors310 to protect the thin-film transistors 310. For example, theprotective layer 325 may include a contact hole through which the firstelectrode 331 of the light-emitting element 330 passes.

The planarization layer 327 may be disposed on the protective layer 325to provide a flat surface over the thin-film transistors 310. Forexample, the planarization layer 327 may include a contact hole throughwhich the first electrode 331 of the light-emitting element 330 passes.The contact hole of the protective layer 325 and the contact hole of theplanarization layer 327 may be connected to each other so as topenetrate the first electrode 331 of the light-emitting element 330.

The emission material layer EML may be disposed on the thin-filmtransistor layer TFTL and may include the light-emitting element 330connected to the thin-film transistor 310 of the thin-film transistorlayer TFTL.

The light-emitting element 330 may include a first electrode 331, anemissive layer 332, and a second electrode 333. The first electrode 331may be disposed on the planarization layer 327. For example, the firstelectrode 331 may overlap the opening of the emission material layer EMLdefined by a pixel-defining layer 340. In addition, the first electrode331 may be in contact with the drain electrode 314 of the thin-filmtransistor 310 through a contact hole formed in the planarization layer327 and the protective layer 325. For example, the first electrode 331may work as an anode of the light-emitting element 330.

The emissive layer 332 may be disposed on the first electrode 331 andmay include a hole injecting layer, a hole transporting layer, aphotosensitive layer, an electron blocking layer, an electrontransporting layer, an electron injecting layer, etc. For example, theemissive layer 332 may include, but is not limited to, an organicemissive layer made of an organic material. If the emissive layer 332 isan organic emissive layer, the thin-film transistor 310 of the thin-filmtransistor TFTL may apply a predetermined voltage to the first electrode331 of the light-emitting element 330, and the second electrode 333 ofthe light-emitting element 330 may receive a common voltage or cathodevoltage. As a result, the holes and electrons may move to the organicemissive layer 332 through the hole transporting layer and the electrontransporting layer, respectively, and combine in the organic emissivelayer 332 to emit light.

The second electrode 333 may be disposed on the emissive layer 332. Forexample, the second electrode 333 may be implemented in the form of acommon electrode extended across all of the pixels SP, instead of beingdisposed separately in each of the pixels SP.

The emission material layer EML may include a pixel-defining layer 340defining a plurality of pixels SP. The first electrode 331 and theemissive layer 332 of the light-emitting element 330 may be spaced apartand insulated from each other by the pixel-defining layer 340.

The first thin-film encapsulation layer TFEL1 may be disposed on theemission material layer EML to cover the thin-film transistor layer TFTLand the emission material layer EML. The first thin-film encapsulationlayer TFEL1 can prevent oxygen or moisture from permeating into theemission material layer EML.

The touch sensor layer TSL may be disposed on the first thin-filmencapsulation layer TFEL1 and may include touch electrodes (for sensinga user's touch) and touch electrode lines for connecting the pads withthe touch electrodes. The touch electrodes of the touch sensor layer TSLmay be disposed in a touch sensing area overlapping the display area DAof the display panel 300.

The cover window 100 may be disposed at the top of the display panel 300and may be disposed on the touch sensor layer TSL of the display panel300. For example, the cover window 100 may be attached on the touchsensor layer TSL by an optically clear adhesive. The cover window 100may be in direct contact with a user's finger F.

The fingerprint sensor layer FPSL may be disposed at the bottom of thedisplay panel 300. For example, the fingerprint sensor layer FPSL may bedisposed under the first substrate SUB1. The upper end of the firstsubstrate SUB1 may face the display panel 300 or the optical layer PHL,and the lower end of the first substrate SUB1 may face the fingerprintsensor layer FPSL. For example, the upper surface of the fingerprintsensor layer FPSL may be attached on the lower surface of the firstsubstrate SUB1 through an adhesive member OCA.

In one embodiment, the first substrate SUB1 may be omitted. In thiscase, the upper surface of the fingerprint sensor layer FPSL may beattached directly to the lower surface of the optical layer PHL by anadhesive member OCA. For example, when the user's finger F is broughtinto contact with the cover window 100, the first light L1 output fromthe emission material layer EML may be reflected by the ridges FR and/orvalleys FV of the finger F, and the reflected second light L2 may passthrough the holes H of the optical layer PHL to reach the fingerprintsensor layer FPSL disposed under the first substrate SUB1.

The fingerprint sensor layer FPSL may include a third substrate SUB3, abuffer layer BF, a photodetector layer PDL, and a second thin-filmencapsulation layer TFEL2. The third substrate SUB3 may be a basesubstrate or a base member of the fingerprint sensor layer FPSL and maybe made of an insulating material such as a polymer resin. The thirdsubstrate SUB3 may be a rigid substrate or a flexible substrate that maybend, fold, or roll. When the third substrate SUB3 is a flexiblesubstrate, it may be made of polyimide (PI) or another material whichallows for bending, folding, or rolling.

The buffer layer BF may be disposed on the third substrate SUB3 and maybe formed of an inorganic film that can prevent or reduce the permeationof air or moisture. For example, the buffer layer BF may include aplurality of inorganic films stacked on one another alternately. Thebuffer layer BF may include, for example, multiple layers, which mayinclude, for example, one or more inorganic layers of a silicon nitridelayer, a silicon oxynitride layer, a silicon oxide layer, a titaniumoxide layer and an aluminum oxide layer alternately stacked on oneanother.

The photodetector layer PDL may be disposed on the buffer layer BF andmay include at least one switching transistor 350 for driving each ofthe plurality of fingerprint sensors FPS, and a photodetector PDconnected to the at least one switching transistor 350.

At least one switching transistor 350 may include a semiconductor layer351, a gate electrode 352, a source electrode 353 and a drain electrode354. The semiconductor layer 351 may be disposed on the buffer layer BF.The semiconductor layer 351 may be disposed to overlap the gateelectrode 352, the source electrode 353, and the drain electrode 354.The gate electrode 352 may be on the first insulating layer 361 and mayoverlap the semiconductor layer 351, with the first insulating layer 361interposed therebetween. The source electrode 353 and the drainelectrode 354 may be disposed on the third insulating layer 365 andspaced apart from each other. The drain electrode 354 may be in directcontact with the first electrode 371 of the photodetector PD through thecontact hole of first to third insulating layers 361, 363 and 365.

The photodetector PD may include a first electrode 371, a photosensitivelayer PSC, and a second electrode 375. The first electrode 371 of thephotodetector PD may be disposed on the second insulating layer 363 andmay be connected to the drain electrode 354 of the switching transistor350 through a contact hole penetrating the third insulating layer 365.For example, the first electrode 371 may be made up of a single layer(e.g., including molybdenum (Mo), titanium (Ti), copper (Cu) or aluminum(Al), etc.) or may be made up of a stack structure (e.g., includingaluminum and titanium (Ti/Al/Ti), a stack structure of aluminum andindium-tin-oxide ITO (ITO/Al/ITO), an APC alloy and a stack structure ofa silver-palladium-copper (APC) alloy and ITO (ITO/APC/ITO)).

The photosensitive layer PSC may be disposed on the first electrode 371.For example, the photosensitive layer PSC may include an n-typesemiconductor layer 372, an i-type semiconductor layer 373, and a p-typesemiconductor layer 374 stacked on one another sequentially. When thephotosensitive layer PSC is formed in a PIN structure including then-type semiconductor layer 372, the i-type semiconductor layer 373 andthe p-type semiconductor layer 374, the i-type semiconductor layer 373may be depleted by the p-type semiconductor layer 374 and the n-typesemiconductor layer 372, and an electric field may be generated insidethe i-type semiconductor layer 373. In addition, holes and electronsgenerated by sunlight may be drifted by the electric field. Accordingly,the holes may be collected to the second electrode 375 through thep-type semiconductor layer 374, and the electrons may be collected tothe first electrode 371 through the n-type semiconductor layer 372.

The p-type semiconductor layer 374 may be disposed closer to theincidence surface of the reflected light, and the n-type semiconductorlayer 372 may be disposed farther from the incidence surface of thereflected light. Since the drift mobility of holes is lower than thedrift mobility of electrons, the p-type semiconductor layer 374 isdisposed closer to the incidence surface of the reflected light, therebyincreasing or maximizing the efficiency of collecting the reflectedlight.

The second electrode 375 of the photodetector PD may be disposed on thep-type semiconductor layer 374 and may be connected to the firstconnection electrode 381 through a contact hole penetrating the thirdinsulating layer 365. The second electrode 375 may include a transparentconductive material capable of transmitting light. For example, thesecond electrode 375 may include, but is not limited to, at least one ofindium tin oxide (ITO), indium zinc oxide (IZO) and indium tin zincoxide (ITZO).

The first connection electrode 381 may be disposed on the third gateinsulating layer 365. For example, the first connection electrode 381may be disposed on the third insulating layer 365 so that it is spacedapart from the source electrode 353 and the drain electrode 354. Thefirst connection electrode 381 may have one end connected to the secondelectrode 375 of the photodetector PD through a contact hole penetratingthe third insulating layer 365, and another end connected to a secondconnection electrode 383 through a contact hole penetrating through thesecond and third insulating layers 363 and 365.

The second connection electrode 383 may be disposed on the firstinsulating layer 361 to overlap the photodetector PD. For example, thesecond connection electrode 383 may be disposed on the same layer as thegate electrode 352 of the switching transistor 350. The secondconnection electrode 383 may be insulated from the first electrode 371of the photodetector PD, with the second insulating layer 363therebetween. The second connection electrode 383 may be connected tothe first connection electrode 381 through a contact hole penetratingthrough the second and third insulating layers 363 and 365.

The photodetector layer PDL may further include first to thirdinsulating layers 361, 363 and 365. The first insulating layer 361 maybe disposed on the semiconductor layer 351. The first insulating layer361 may cover the semiconductor layer 351 of the switching transistor350 and the buffer layer BF and may insulate the semiconductor layer 351from the gate electrode 352.

The second insulating layer 363 may be disposed on the gate electrode352 of the switching transistor 350 and the second connection electrode383. The second insulating layer 363 may cover the gate electrode 352,the second connection electrode 383, and the first insulating layer 361.The second insulating layer 363 may insulate each of the sourceelectrode 353 and the drain electrode 354 from the gate electrode 352,and may insulate the first electrode 371 of the photodetector PD fromthe second connection electrode 383.

The third insulating layer 365 may be disposed on the photodetector PDand may cover the photodetector PD and the second insulating layer 363.

The second thin-film encapsulation layer TFEL2 may be disposed on thephotodetector layer PDL and may cover the source electrode 353 and thedrain electrode 354 of the switching transistor 350, the firstconnection electrode 381, and the third insulating layer 365. The secondthin-film encapsulation layer TFEL2 can prevent or reduce oxygen ormoisture from permeating into the photodetector layer PDL. The uppersurface of the second thin-film encapsulation layer TFEL2 may beattached to the lower surface of the first substrate SUB1 by an adhesivemember OCA.

The controllers, processors, drivers, units, and other signal generatingand signal processing features of the embodiments disclosed herein maybe implemented, for example, in non-transitory logic that may includehardware, software, or both. When implemented at least partially inhardware, the controllers, processors, drivers, units, and other signalgenerating and signal processing features may be, for example, any oneof a variety of integrated circuits including but not limited to anapplication-specific integrated circuit, a field-programmable gatearray, a combination of logic gates, a system-on-chip, a microprocessor,or another type of processing or control circuit.

When implemented in at least partially in software, the controllers,processors, drivers, units, and other signal generating and signalprocessing features may include, for example, a memory or other storagedevice for storing code or instructions to be executed, for example, bya computer, processor, microprocessor, controller, or other signalprocessing device. The computer, processor, microprocessor, controller,or other signal processing device may be those described herein or onein addition to the elements described herein. Because the algorithmsthat form the basis of the methods (or operations of the computer,processor, microprocessor, controller, or other signal processingdevice) are described in detail, the code or instructions forimplementing the operations of the method embodiments may transform thecomputer, processor, controller, or other signal processing device intoa special-purpose processor for performing the methods described herein.

Although described with reference to exemplary embodiments of thepresent disclosure, it will be understood that various changes andmodifications of the present disclosure may be made by one ordinaryskilled in the art or one having ordinary knowledge in the art withoutdeparting from the spirit and technical field of the present disclosureas hereinafter claimed. Hence, the technical scope of the presentdisclosure is not limited to the detailed descriptions in thespecification but should be determined only with reference to theclaims. The embodiments may be combined to form additional embodiments.

What is claimed is:
 1. A fingerprint sensor comprising: a photodetector;a first transistor configured to connect a second node with a third nodebased on a voltage of a first node, the first node corresponding to afirst electrode of the photodetector; a second transistor configured toconnect the second node with a read-out line based on a scan signal; athird transistor configured to supply a reset voltage to the first nodebased on a first reset signal; and a fourth transistor configured toconnect the first node with the second node based on a second resetsignal.
 2. The fingerprint sensor of claim 1, wherein: the firstelectrode of the photodetector is connected to a gate electrode of thefirst transistor, and a second electrode of the photodetector isconfigured to receive a bias voltage.
 3. The fingerprint sensor of claim1, further comprising: a fifth transistor configured to supply a commonvoltage to the third node based on the scan signal; and a sixthtransistor configured to supply a sampling voltage to the third nodebased on the second reset signal.
 4. The fingerprint sensor of claim 3,wherein the third transistor is configured to turn on during a firstperiod to supply the reset voltage to the first node.
 5. The fingerprintsensor of claim 4, wherein the fourth transistor is configured to turnon during a second period after the first period, to connect the firstnode with the second node.
 6. The fingerprint sensor of claim 4, whereinthe sixth transistor is configured to turn on during a second periodafter the first period, to apply the sampling voltage to the third node.7. The fingerprint sensor of claim 5, wherein the photodetector isconfigured to receive reflected light during a third period after thesecond period, to allow flow of a current of the first node.
 8. Thefingerprint sensor of claim 7, wherein the fifth transistor isconfigured to turn on during a fourth period after the third period, toapply the common voltage to the third node.
 9. The fingerprint sensor ofclaim 7, wherein the first transistor is configured to supply an outputcurrent to the second node based on a voltage of the first node during afourth period after the third period.
 10. The fingerprint sensor ofclaim 7, wherein the second transistor is configured to connect thesecond node with the read-out line during a fourth period after thethird period.
 11. A display device, comprising: a display layerconfigured to emit light to display an image; a fingerprint sensor layeron a surface of the display layer, the fingerprint sensor layercomprising a plurality of fingerprint sensors, each of the plurality offingerprint sensors configured to receive reflected light to generate asensing signal; and a sensor driver configured to receive the sensingsignals from the plurality of fingerprint sensors through correspondingones of a plurality of read-out lines, wherein each of the plurality offingerprint sensors comprises: a photodetector; a first transistorconfigured to connect a second node with a third node based on a voltageof a first node that corresponds to a first electrode of thephotodetector; a second transistor configured to connect the second nodewith a corresponding one of the plurality of the read-out lines based ona scan signal; a third transistor configured to supply a reset voltageto the first node based on a first reset signal; and a fourth transistorconfigured to connect the first node with the second node based on asecond reset signal.
 12. The display device of claim 11, wherein each ofthe plurality of fingerprint sensors comprises: a fifth transistorconfigured to supply a common voltage to the third node based on thescan signal; and a sixth transistor configured to supply a samplingvoltage to the third node based on the second reset signal.
 13. Thedisplay device of claim 12, wherein the third transistor is configuredto turn on during a first period to supply the reset voltage to thefirst node.
 14. The display device of claim 13, wherein: the fourthtransistor is configured to turn on during a second period after thefirst period to connect the first node with the second node, and thesixth transistor is configured to turn on for the second period to applythe sampling voltage to the third node.
 15. The display device of claim14, wherein: the first electrode of the photodetector is connected to agate electrode of the first transistor, a second electrode of thephotodetector is configured to receive a bias voltage, and thephotodetector is configured to receive the reflected light during athird period after the second period, to allow a current to flow fromthe first electrode to the second electrode.
 16. The display device ofclaim 15, wherein: the fifth transistor is configured to supply thecommon voltage to the third node during a fourth period after the thirdperiod, the first transistor is configured to supply an output currentto the second node based on the voltage of the first node during thefourth period, and the second transistor is configured to connect thesecond node with the read-out line during the fourth period.
 17. Thedisplay device of claim 11, further comprising: an optical layer betweenthe display layer and the fingerprint sensor layer, wherein the opticallayer comprises a plurality of holes.
 18. The display device of claim11, wherein the first electrode of the photodetector is disposed on abase of the fingerprint sensor layer and is connected to a firstelectrode of the third transistor or a first electrode of the fourthtransistor.
 19. The display device of claim 18, wherein thephotodetector comprises: a photosensitive layer on a surface of thefirst electrode; and a second electrode disposed on a surface of thephotosensitive layer and configured to receive a bias voltage.
 20. Thedisplay device of claim 19, wherein the second electrode comprises atransparent conductive layer.